JPH0650710B2 - Method for manufacturing solid electrolytic capacitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a solid electrolytic capacitor having good performance, which uses a conductive polymer compound as a solid conductor.

[Prior Art] In a conventional solid electrolytic capacitor, for example, an aluminum electrolytic capacitor, an aluminum oxide layer as a dielectric is provided on a porous aluminum foil having a large specific surface area that has been subjected to etching treatment, and an electrolytic paper between the cathode foil and Although it has a structure impregnated with a liquid electrolyte, it is not preferable because it causes a problem such as liquid leakage because the electrolyte is liquid,
Therefore, attempts have been made to replace this conductive layer with a solid conductor. These solid electrolytic capacitors have a structure in which a solid conductor is attached to a film-forming metal such as aluminum or tantalum having an anodized film, and the solid conductor of this type of solid capacitor is mainly composed of manganese nitrate. Manganese dioxide formed by thermal decomposition is used. However, in this solid electrolytic capacitor, due to the high heat required for thermal decomposition and the oxidizing action of NO _x gas generated, the metal oxide film such as aluminum and tantalum, which is a dielectric, is damaged, and the withstand voltage is lowered. However, there is an extremely large defect that the leakage current becomes large and the dielectric characteristics are deteriorated.

In order to compensate for these drawbacks, a method of using a highly conductive organic semiconductor material as a solid conductor has been attempted as a method of forming a solid conductor without applying high heat. As an example, as described in JP-A-52-79255, 7,7,8,8
There is known a solid electrolytic capacitor in which a conductive organic compound containing a tetracyanoquinodimethane (TCNQ) complex salt is a main component of a solid conductor. However, in this solid electrolytic capacitor, the TCNQ complex salt is inferior in adhesion to the anodic oxide coating and the electric conductivity is insufficient as 10 ⁻³ to 10 ⁻² S / cm.
The capacitance value of the capacitor is small, the dielectric loss is large, the thermal stability over time is poor, and the reliability is low. Also, TCN
Since the Q complex salt is expensive, there is a problem that the manufacturing cost of the solid electrolytic capacitor as a whole is high.

In recent years, attempts have been made to provide a solid electrolytic capacitor having a high conductivity, good adhesion to a dielectric film, and an inexpensive conductive polymer compound as a solid conductor. In this attempt, the conductive polymer compound was skillfully introduced into the pores of the porous metal oxide when the conductive polymer compound was deposited on the film of the porous metal oxide used as the dielectric. Stabilization is the most important issue. In general, a conductive polymer compound is insoluble and infusible, and is extremely inferior in shapeability and processability. For this reason, most conductive polymer compounds cannot be melt-molded or molded by the casting method, so that they should be introduced into the pores of the porous metal oxide while having excellent performance as a solid conductor. In many cases, it cannot be used for solid electrolytic capacitors.

[Problems to be Solved by the Invention] An object of the present invention is to solve the above-mentioned problems of the prior art,
A conductive polymer compound, which has excellent performance as a solid conductor, can be easily introduced into the pores of the porous dielectric, and the adhesion to the dielectric film is good, and the manufacturing cost is low. It is an object of the present invention to provide a method for manufacturing a solid electrolytic capacitor which uses a conductive polymer compound as a solid conductor.

[Means for Solving Problems] According to the present invention, in producing a solid electrolytic capacitor using a conductive polymer compound as a solid conductor, the conductive polymer compound is partially exposed to a porous metal. The present invention is characterized in that electrolytic polymerization is carried out starting from the metal surface of a porous dielectric material to deposit and grow on the surface of the porous dielectric layer, and then a dielectric layer is formed on the exposed metal surface by anodic oxidation. A method for manufacturing a solid electrolytic capacitor is provided.

In the method of the present invention, the conductive polymer compound used as a solid conductor to be deposited and grown on the surface of the porous dielectric layer by electrolytic polymerization starting from the metal surface of the partially exposed metal porous dielectric, It is a polymer compound having a π-electron conjugated system, and one having an electric conductivity of 10 ⁻³ S / cm or more is desirable. Typical examples of such conductive polymer compounds include polyacetylene, polyparaphenylene, polypyrrole, pothiophene, polycyanoacetylene, polyisothianaphthene, polydiacetylene, polyaniline, polyphthalocyanine and dielectrics of monomers constituting these polymers. Examples thereof include polymers of the body. Among these conductive polymer compounds, preferred conductive polymer compounds include polythiophene, poly (1,3-isothianaphthene), and polypyrrole, and more preferably polythiophene.

Among the above conductive polymer compounds, 10 ^{-3 in the} neutral state
Some have an electrical conductivity of S / cm or more, and some have an electrical conductivity of 10 ^-3 S / cm or more by doping with an electron donating or electron withdrawing dopant.
Any of them can be used as a solid conductor.

In the latter case, the doping may be either chemical doping or electrochemical doping. As the chemically doped dopant, various conventionally known electron-accepting compounds and electron-donating compounds,
For example, (I) iodine, halogen such as bromine and bromine iodide,
(II) Metal halides such as arsenic pentafluoride, antimony pentafluoride, silicon tetrafluoride, phosphorus pentachloride, phosphorus pentafluoride, aluminum chloride, aluminum bromide and aluminum fluoride, (II
I) Protic acids such as sulfuric acid, nitric acid, fluorosulfuric acid, trifluoromethane sulfuric acid and chlorosulfuric acid, (IV) Sulfur trioxide, nitrogen dioxide, oxidizing agents such as difluorofurfonyl peroxide, (V) AgClO ₄ , (VI) tetra Cyanoethylene, tetracyanoquinodimethane, chloranil,
2,3-dichloro-5,6-dicyanoparabenzoquinone, 2,3
-Dibromo-5,6-dicyanoparabenzoquinone, (VII)
Alkali metals such as Li, Na and K can be used. On the other hand, as the dopant to be electrochemically doped, (I) PF, SbF, AsF, SbCl
Halide anions of Va group elements such as BF
Halide anions of group IIIa elements such as I,
^{- (I), Br -,} Cl - such halogen anions,
Anion dopants such as perchlorate anions such as ClO and (II) Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , Cs ⁺
Alkali metal ions such as R _{4, X} M ⁺ H _X or R ₃ M ₁ ⁺ [wherein R is a C ₁ to C ₁₀ alkyl group, an aryl group such as phenyl, halophenyl, alkylphenyl, and M is N, P, As, M ₁ is 0 or S, x is 0
Or represents 1. ] Tetraalkylammonium ions, tetraalkylphosphonium ions, tetraalkylarsonium ions, trialkyloxonium, trialkylsulfonium ions, and other cations / dopants, etc. can be mentioned, but are not necessarily limited to these is not.

The type of the porous dielectric material used in the present invention is not particularly limited, but for example, an oxide of a metal such as aluminum, tantalum or niobium can be preferably used. There is no particular limitation on the method of partially exposing the metal surface to the porous dielectric, and for example, by using the metal surface generated when the porous dielectric is cut, or by exposing the metal surface in spots on one surface. Can be used.

The surface area of the metal exposed portion of the porous dielectric cannot be determined unconditionally because it varies depending on the type of the monomer for polymerization that gives the conductive polymer compound, but it is generally 0.001 to 10 with respect to the total surface area of the porous dielectric. %, Preferably 0.01 to 5%.

The electrolytic polymerization method in the present invention is, for example, a method of electrolyzing an electrolytic solution containing a monomer for polymerization to give the conductive polymer compound, and performing oxidative polymerization of the monomer, which is known for various monomers for polymerization. This can be done by selecting appropriate polymerization conditions. In the electrolytic polymerization method known so far, as the anode, an electrochemically stable material such as gold or platinum is used, but in the present invention, as described above, the metal is partially exposed. A porous dielectric is used. The polymerization reaction proceeds rapidly starting from this metal surface, and the conductive polymer compound grows so as to cover the surface of the dielectric.

The polymerization temperature of electrolytic polymerization is not particularly limited, but in general-
It is carried out at temperatures between 60 ° C and 80 ° C, preferably between -20 ° C and 30 ° C.

The polymerization time is appropriately selected by observing and determining the degree of precipitation / growth of the conductive polymer compound, but it is generally several minutes to several hours.

The polymerization pressure is not particularly limited, but generally, the inside of the pores of the porous dielectric layer is filled with the electrolytic solution by a depressurization operation before the initiation of the polymerization, and then the pressure is returned to normal pressure to carry out the polymerization operation.

As anodization (post chemical conversion) for repairing the metal surface of the porous dielectric where the metal is partially exposed after polymerization,
It is performed by non-aqueous system, aqueous system, solid phase system, etc.
A suitable system can be selected depending on the kind of the conductive polymer compound.

[Effects of the Invention] The solid electrolytic capacitor manufactured by the method of the present invention is remarkably excellent in capacity, dielectric loss, and stability over time as compared with conventional solid electrolytic capacitors using an inorganic oxide semiconductor or an organic semiconductor. Has performance.

The solid electrolytic capacitor manufactured by the method of the present invention has the following advantages as compared with the conventionally known solid electrolytic capacitors.

Since the conductive polymer compound can be formed on the porous dielectric layer without heating to a high temperature, the oxide film of the anode is not damaged. Therefore, the rated voltage can be increased several times that of the conventional one, and to obtain a capacitor with the same capacity and rated voltage,
The shape can be made smaller than the conventional one.

Since the adhesion between the conductive polymer compound and the dielectric film is good, the leakage current is small.

A high breakdown voltage capacitor can be manufactured.

Since the electric conductivity of the conductive polymer compound is sufficiently high at 10 ⁻³ S / cm or more, it is not necessary to provide a conductive layer such as graphite, and the process therefor can be simplified.

Good frequency characteristics.

Manufacturing cost is low.

[Examples] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

The characteristic values of the solid electrolytic capacitors of each example are shown in the table.

Example 1 An aluminum foil having a thickness of 100 μm (purity 99.99%) was used as an anode, and the surface of the foil was electrochemically etched by alternating use of direct current and alternating current to have an average pore diameter of 2 μm and a specific surface area of 2 μm.
It was 12 m ² / g of porous aluminum foil. Next, this etched aluminum foil was immersed in a solution of ammonium borate to electrochemically form a thin layer of a dielectric on the aluminum foil in the solution.

The aluminum metal surface was partially exposed by cutting the outer peripheral portion of the aluminum foil thus produced. The exposed portion of aluminum metal was 0.1% of the total surface area of the porous dielectric. Using this as an anode, a platinum plate as a cathode, and a benzonitrile solution containing 0.1 mol / thiophene and 0.05 mol / LiBF ₄ in an argon gas atmosphere at room temperature and atmospheric pressure at 4 to 5 V for 2 m.
A current of A / cm ² was applied for 2 hours to electrochemically polymerize thiophene to deposit a polythiophene film on the anode plate. The conductivity of this polythiophene film is 20S
It was / cm. Next, the aluminum foil covered with this polythiophene film was used as an anode, and the platinum plate was used as a cathode.
Post chemical conversion was carried out at 9 V for 10 minutes in a solution of ammonium borate in ethylene glycol. After this, the chemical compound is used as an anode,
Aluminum foil was used for the cathode and sealed with rubber to produce a solid electrolytic capacitor.

Example 2 Using the same anode as in Example 1 but using a carbon plate as the cathode, 0.1 mol / l of 1,3-isothianaphthene and 0.05 mol
/ 3 Tetraphenylphosphonium chloride in an acetonitrile solution containing argon gas at room temperature and atmospheric pressure with a current of 2 to 3 V and 1 mA / cm ² for 2 hours to electrochemically polymerize isothianaphthene. A polyisothianaphthene film was deposited on the anode plate. The conductivity of this poly (1,3-isothianaphthene) film is
It was 10 S / cm. After post-chemical formation in the same manner as in Example 1, an aluminum foil was used as the cathode and sealed with rubber to produce a solid electrolytic capacitor.

Example 3 Using the same anode as in Example 1 and using a platinum plate as the cathode, a solution of acetonitrile containing 0.1 mol / pyrrole and 0.05 mol / tri-n-butylammonium salt of p-toluenesulfonic acid was prepared. In an argon gas atmosphere, at room temperature,
A current of 3 to 4 V and 1 mA / cm ² was applied at normal pressure for 2 hours to electrochemically polymerize pyrrole to deposit a polypyrrole film on the anode plate. The conductivity of this polypyrrole film was 50 S / cm. After post-chemical formation in the same manner as in Example 1, an aluminum foil was used as the cathode and rubber sealing was performed to produce a solid electrolytic capacitor.

Comparative Example Using the aluminum foil having the same dielectric layer as that of Example 1, a conventional solid electrolytic capacitor was prepared in which conventional manganese dioxide was used as the solid conductor and the cathode was the aluminum foil.

Claims (1)

[Claims] 1. When producing a solid electrolytic capacitor using a conductive polymer compound as a solid conductor, electrolytic polymerization is carried out by using the conductive polymer compound as a starting point from a metal surface of a porous dielectric having a partially exposed metal. By depositing and growing on the surface of the porous dielectric layer, and then forming the dielectric layer on the exposed metal surface by anodic oxidation.